1. Field of the Invention
The present invention relates to a constant velocity universal joint which is used, for example, to couple a first transmission shaft and a second transmission shaft at a driving force-transmitting section of an automobile. The present invention also relates to a method for assembling such a constant velocity universal joint.
2. Description of the Related Art
A constant velocity universal joint has been hitherto used for a driving force-transmitting section of an automobile, for coupling a first transmission shaft and a second transmission shaft so that the rotary force is transmitted to each axle.
Such a constant velocity universal joint concerning the conventional technique is shown in FIGS. 67 and 68 (see Japanese Laid-Open Patent Publication No. 7-103251).
The constant velocity universal joint 1 comprises mutually opposing guide tracks 2a, 2b which are formed on an inner wall surface of an outer joint 3. A spherical tripod journal 4 is arranged between the guide tracks 2a, 2b. An inner roller 5 is externally fitted to the tripod journal 4. An outer roller 7 is supported via a plurality of needle bearings 6 on an outer circumferential surface of the inner roller 5.
In this arrangement, surfaces 8a, 8b, 9a, 9b, which extend substantially in parallel to the axis of the tripod journal 4, are formed on the circumferential surfaces of the tripod journal 4 and the outer roller 7 on the both opposing sides in the rotational direction of the joint. The surfaces 8a, 8b, 9a, 9b function such that the force, which is applied to the tripod journal 4 and which is effective in the circumferential direction, is divided into two components of force. Owing to such an arrangement, the improvement in distribution of the contact surface pressure is achieved under the load of torque.
However, in the case of the constant velocity universal joint 1 concerning the conventional technique described above, for example, each of the components of force F1, F2, which is applied to the inner roller 5 by the surface 8b formed on the circumferential surface of the tripod journal 4, is composed of a relatively high load. Therefore, an inconvenience arises in that the contact surface pressure (force to press the contact surface), which is exerted in the direction of the arrow between the tripod journal 4 and the inner roller 5, is increased as compared with the contact surface pressure on other circumferential surfaces. This results in a problem that the durability is deteriorated.
Further, the constant velocity universal joint 1 concerning the conventional technique comprises the inner roller 5 and the outer roller 7 held by the guide tracks 2a, 2b via the needle bearings 6. The tripod journal 4 is provided such that it makes displacement in the vertical direction along the inner wall surface of the inner roller 5 held by the guide tracks 2a, 2b. Therefore, the constant velocity universal joint 1 concerning the conventional technique is inconvenient in that it is impossible to reduce the slide resistance on the sliding surface between the tripod journal 4 and the inner roller 5.
A general object of the present invention is to provide a constant velocity universal joint which makes it possible to improve the durability by decreasing the contact surface pressure on the contact surface between a trunnion and an annular member externally fitted to the trunnion.
A principal object of the present invention is to provide a constant velocity universal joint which makes it possible to further improve the induced thrust performance by reducing the slide resistance generated when a first transmission shaft is inclined and a trunnion is displace along a guide groove.
Another object of the present invention is to provide a constant velocity universal joint which makes it possible to further improve the strength of a trunnion without inhibiting the assembling performance when an annular member is externally fitted to the trunnion.
Still another object of the present invention is to provide a method for assembling a constant velocity universal joint, which makes it possible to conveniently assemble a trunnion provided with a spherical surface and an annular member formed with a recess corresponding to the spherical surface of the trunnion.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.